Direct fired oil heater



' .March 12, 1940. I c; s REED AL Re. 21,396

DIRECT FIRED OIL HEATER Original Filed Sept. 8, 1932 4 Sheets-Sheet lOOOGOOOm /ooooooo 25 EV E 6 G Z 79 97 6 O a O [2 [3 0 Z O O O gm o o g 0a, ()Z,. ---/Z 0 9 6 V O OOOOOOQOOCZ DOO' Z l IINVENTOR Carl 5. e294Vincent Weaver Smith March 12, 1940. c. s. REED ET AL DIRECT FIRED OILHEATER Original Filed Sept. 8, 1932 4 Sheets-Sheet 2 .m m s m M n m wINVENTOR Carl 5. Pied March 12, 1940. c, s, REED ET AL.

DIR CT FIRED on. HEATER Original Filed Sept. 8, 1932 4 Sheets-Sheet 3ooooofiwooooo H OOOOORmW VOOOO INVENTORS Carl 5. Reed Vincent Mal erSmith yfieir' zfta neg 44,17

March 12, 1940. c REED ET AL Re. 21,396

DIRECT FIRED OIL HEATER Original Filed Sept. 8, 1932 4 Sheets-Sheet 4INVE Rs Ca r! Reed Vince/2t I'VeawrSmiLf/z %fieir ZttOI-Zy Reiaued Mar.12, 1940 UNITED STATES PATENT OFFICE nmso'rrmlnomnssmOarl8.Beedan|iVi:,eentW.lmith,New

N. 1., allignors New york, N. Y., a

m. The Lunnnus mmmolnelaware a Glainis. (a. 190-110) Our inventionrelates to a heater for fluids and is particularly useful for heatingoil to be refined or cracked. However, the invention is not restrictedto such use.

of a direct fired fluid heater wherein substantially all of the heatcarried to the fluid is transmitted by radiation. Another object is theprovision of such a heater wherein the heat of combustion may betransferred substantially by radiation alone to exposed tubes in theheater sides which carry the, fluid to be heated. A further object isthe construction of a heater wherein the rate of heat absorption at thepoint of exit appear upon consideration of the present specification.

The invention is shown by way of illustration in the accompanyingdrawings wherein- Flgure 1 is a vertical cross-section of the heater,

Fig. 2 is a longitudinal vertical section on the line 11-11 of theheater illustrated in Figure l, Flg. 3 is a vertical cross-section ofthe lower part of a modified form of heater,

Fig. 4 is a vertical cross-section of part of the heater showing amodified form of roof wherein a row of tubes functions as a diffusionbailie,

Fig. 5 is a vertical cross-section of part of the heater showing anothermodified form of roof,

Fig. 6 is a vertical cross-section of part of the heater showing stillanother modified form of roof, and

Fig. 7 is a fragmental view illustrating one of the bifurcated tubesused in the roof illustrated in Fig. 6.

In heating oil it is necessary to regulate the degree of heat which isapplied to the tubes containing the oil to be heated. It is furthernecessary to control the rate at which heat is carried to the tubes. Inthe past it has been considered good practice to prevent radiant heat Ifrom reaching the tubes carrying the oil, and heaters have accordinglybeen constructed so that the combustion gases are carried to the oiltubes in such a way as to eliminate the effects of radiation, and toheat these tubes substantially by convection alone. When attempts havebeen made to transfer heat by radiation at comparatively high ratesdifilculties have been encountered. The oil has been decomposed throughlocal overheating and the desired product has not been obtained. Thishas been particularly true at the part of the furnace where thecombustion gases are discharged. We have now discov- One object of theinvention is the provision from the heater is controlled. Other objectswill ered that highly desirable results may be obtained by carrying heatto the oil tubes by radiation alone and by controlling the rate ofcombustion and the rate of travel of the combustion gases out of thefurnace. In the present invention means is provided for preventingexcessive heating at or adjacent the point of exit of the combustiongases.

Referring now more particularly to the drawings, there is shown afurnace l0 and exposed tubes II in the sides of the furnace. The word"sides is used to denote the bounding surfaces of the furnace includingthe fioor and the roof. As here shown, the tubes in the walls are heldin position by supporting members lLat intervals along the wall. whilethe floor tubes merely rest directly on the floor, and the roof tubesare otherwise suspended, as will be later explained.

Burners are provided for projecting fuel and air into the furnace I0.Such burners may be oil or gas burners l3 extending through two oppositewalls of the furnace, as illustrated in Fig. 2. The burners illustratedin Fig. 2 project through walls which have no tubes upon them, and throwa jet of fuel toward the middle of the furnace. The result is a greaterheating effect near the middle of the furnace and a resulting tendencyfor the tubes to be cooler adjacent the walls through which the burnersproject. Instead of cooling these walls with heat absorbing tubes,however, they are left substantially uncooled and the ends of the walltubes adjacent these substantially uncooled walls thus have theirtemperature'raised by radiation from these walls. Furthermore, such aconstruction makes it easy to dispose the burners as desired sinceprovision need not be made for displacing wall tubes adjacent theopening for each burner.

On the other hand these burners may project through the floor of thefurnace, as shown at It in Fig. 3, or through any side.

Thus the tubes ii on the walls and fioor provide means for abstractingheat adjacent the zone of combustion, and abstraction takes placesubstantially entirely by radiation, as will be more fully explained.

To avoid the possibility of overheating tubes exposed to both directradiation and convection, one of the sides of the furnace, preferablythe roof I4, is open over its entire area, except for tubes I lextendingthereacross, providing a. heating gas outlet of substantial flow area.As shown.

in Fig. l, the roof tubes II. are arranged in two,

staggered rows, the tubes I i being parallel to-andl of the same lengthas the other wall andvfloor convection heat transfer thereto.

Above the roof tubes II' is provided a fiow equalizing or plenum chamber25 of substantial volume in which the heating gases collect afterpassing over the roof tubes and before entering the convection heatingsection of the heater. The convection heating section is formed by arelatively shallow bank of staggered rows of I us tubes l6 extendingparallel to and of the same length as the tubes and ii. Effective heattransfer conditions for the tubes it are maintained by causing ahorizontal fiow of the heating gases transversely of the tubes, and forthis ber must first pass around the baiile 26 and horizontally acrossthe bank of tubes I8 before reaching the gas outlet.

To avoid local overheating of the tubes ll due to laning or channellingof the low velocity heating gases relative thereto, a diffusion bailieis arranged at the outer side of the lower row of tubes II' with the gasfiow passages therein uniformly distributed and of less aggregate flowarea than the aggregate intertube area of the sub-' jacent portions ofthe lower row of tubes Il thereby providing a pressure drop betweenopposite sides of the baiiie which will cause the low velocity heatinggases to flow uniformly past all of the tubes ll in the lower row. Sucha baflie I1 is shown in Figure 1 above the double row of roof tubes H,beingcomp'osed of tile or other suitable material having openings l8distributed substantially uniformly over the entire area. This baiiieperforms two functions-it presents a restricted area for the outlet ofthe hot gases which insures slow travel of the combustion gases throughthe furnace proper particularly past the roof tubes; it also distributesthe openings uniformly over the entire bafiie surface, thus providing auniform flow of heating gases across the roof tubes.

The effective flow area of the openings I! in the bailie I1 isadvantageously adjustable to regulate the pressure drop through thediffusion baiile as desired. Slidabie tile 19 are positioned on the bameH with openings 20 therein distributed to register with those in thebaiiie l1, and being operable by means of externally extending rods 2|,whereby the position of the tile I! may be altered to increase ordecrease the effective flow area of the openings I. in the baiiie.

, Instead of employing a separate diffusion baffle supported on theupper row of roof tubes, the same effect may be produced by a specialconstruction of these roof tubes. Thus, in Fig. 4

this upper, row comprises tubes ,ll" which are spaced on closer centersthan the tubes in the lower row. Thus a pressure drop between the lowerside and the upper side of the upperrow of.

reason of the gases passing between them at a higher velocity than theypass between'the tubes a f in the lower row.. When two or more rows of-I6 tubes are subjected to radiation the inner row of tubes abstracts alarger percentage of the total radiation to the tubes which are exposedthan do the rows beyond. Increasing the velocity of gases past thesecond row tends to increase the heat pick-up of the second row of tubesby adding convection effects to radiation.

In Fig. 5 another form of roof is shown wherein the diffusion baiile isformed by tubes having radial longitudinal fins thereon. The openingsbetween fins on adjacent tubes may be regulated by turning the tubes asillustrated in Fig. 5; and when the furnace is constructed the tubes Iiare turned as shown and fixed to give the desired p nings.

Instead of using fin tubes in the outer row of tubes forming the side ofthe heater through which the combustion gases escape, we may employbifurcated tubes 1 I and such an arrangement is illustratedin Figs. 6and "I. Here again the tubes are turned upon their central axes andfixed in order to give the desired area of opening. A difi'usion battleis thus defined having 'distributed gas flow passages therein of lessaggregate flow area than the aggregate intertube area of the inner rowof tubes ll Means is also provided for controlling the rate ofcombustion in the furnace in order to control the degree of oil heatingin the tubes. Such means is here illustrated by valves 22 and dampers 23respectively, which regulate the rate at which fuel and air enter thefurnace.

In operation the fuel valves 22 are opened, the fuel is ignited and theair supply member opened so that each burner projects a flame into thefurnace either. through vertical side walls as shown in Fig. 2, orthrough the floor as shown in Fig. 3. The openings I! in the diffusionbaffle are adjusted to regulate the rate of passage of the combustiongases through the furnace, and oil is circulated through the tubes H andII in the furnace sides. The rate of combustion and the rate of travelof the gases are then adjusted to give the desired degree of heating.Where the upper row of tubes acts as the diffusion battle, the openingsare a part of the furnace design and are fixed when the furnace isbuilt.

In the construction'whichhas been described the transfer of heat takesplace substantially entirely by radiation. The travel .of the combustiongases takes place at such a rate that very little convection effectresults. The tubes in the roof of the furnace (or in the exit side,where the gases do not leave the furnace at the roof) are spaced atsufficient intervals to prevent a rapid flow of gases past the lower rowof tubes. The restricted exit areas in the diffusion baiiie above theroof tubes are such as to prevent rapid passage of gases past thesetubes, and also such as to insure a uniform distribution of the gasesacross the roof tubes. The result is a heat transfer wherein convectionplays a very slight part except in the second row of roof tubes asexplained above. While the fluid to be heated preferably enters at thecooler end of the convection bank I! and passes successively through thetubes l8, roof tubes, side wall tubes and fioor tubes in the ordernamed, other connections may be made between the various tube groups.

It will be obvious that this form of heater lends itself easily to atwo-stream flow of liquid through the heater, the heating in the twostreamsbeing at a substantially uniform rate and to the same finaltemperature throughout. Thus one may flow serially through half thetubesil.halfoftherooftubes.andonegrcupofwalltubelandhalfoftheiioortubes, whilethe other stream flows through theremaining half of the heating surface.

While specific reference has been made herein to the heating of oil, itis to be understood that the furnace herein described and claimed .iscapable of use in other connections. Water or some other fluid may bepassed through the tubes in the furnace walls, and the degree of heatingmay be appropriately regulated with great ease.

The invention is not limited to the precise construction or applicationherein defined. Other forms and usesof the invention which, do notdepart from the proper scope of the appended claims will readily suggestthemselves to those dealing with problems of heat transfer.

with this understanding, we claim:

1. In a fuel-fired heater, radiant heat absorbing tubes forming one sidethereof. a gas exit from the heater beyond the tubes and other tubeshaving longitudinal fins thereon forming a difi'usion bafiie beyond saidtubes which form the furnace side, adjacent baiiie tubes having narrow.

spaces between the fins thereon whereby the rate of gas flow past theradiantly heated tubes is controlled.

2. A fluid heater comprising a furnace chamber having a heating gas exitoccupyin a major portion of the area of one of the boundary wallsthereof, a row of bare fluid heating tubes extending across said gasexit in transversely spaced relation and in position to receive radiantheat directly from said furnace chamber, and means forming a diffusionbaiiie having distributed gas flow passages therein at the outer side ofsaid rowof tubes, and means for varying the effective flow area throughsaid diffusion bafiie passages.

3. An oil heater comprising a box-shaped furnace chamber having arow ofhorizontally extending oil heating tubes extending across a heating gasexit in one side of and in position to receive radiant heat from saidfurnace chamber, and a row of bifurcated tubes at the outer side of saidfirst row of tubes and arranged to form a diffusion baflie havingdistributed gas flow passages therein of less aggregate flow area thanthe aggregate intertube area of said first row of tubes.

4. An oil heater comprising walls forming a furnace chamber ofsubstantially rectangular horizontal and vertical cross-section, groups'of serially connected horizontal tubes along pposite side walls of saidfurnace chamber, a plurality of staggered rows of horizontal tubesacross the roof of said furnace chamber, fuel burners mounted in the endwalls of said furnace chamber and arranged to discharge streams of fueltowards the center of said furnace chamber, a gas exit flue openingthrough the roof of said furnace chamber, a bank of convection heatedtubes positioned in said flue, and diifusion bafflemeans extendingacross said roof immediately superjacent said roof tubes for maintaininga uniform distribution of heating gases at a low velocity across thelowermost row of tubes posi tioned across said roof opening.

5. An oil heater comprising a box-shaped furnace chamber having a row ofhorizontally extending oil heating tubes extending across a heating gasexit in one side of and in positionto receive radiant heat from saidfurnace chamber, and a second row of tubes having fins extending alongopposite sides thereof and arranged to form a diffusion bailie havingdistributed gas flow passages therein'of less aggregate flow area thanthe aggregate intertube area of said first row of tubes.

6. An oil heater comprising a box-shaped furnace chamber havinghorizontally extending oil heating tubes extending across the roofthereof and in position to receive radiant heat from said furnacechamber, a heating gas exit in said roof and across which said rooftubes extend, means forming a diffusion baiiie at the upper side of saidroof tubes having gas flow passages therein of less aggregate flow areathan the spaces between the subjacent roof tubes, means forming a plenumchamber above said diflusion baiiie, a convection heated bank of fluidheating tubes above said plenum chamber, and a horizontal baliieseparating said tube bank and plenum chamber and arranged to cause theheating gases to enter said tube bank at one side thereof and flowhorizontally thereacross, and a heating gas exit at the opposite side ofsaid tube bank.

'I. An oil heater comprising a box-shaped furnace chamber havinghorizontally extending all heating tubes extending along oppositevertical side walls and the roof thereof, a heating gas exit occupying amajor portion of the roof area and across which said roof tubes extend,means forming a plenum chamber above said roof tubes, a convectionheated bank of fluid heating tubes above said plenum chamber, ahorizontal baflie separating said tube bank and plenum chamber andarranged to cause the heating gases to enter said tube bank at one sidethereof and flow horizonally thereacross, and a heating gas exit at theopposite side of said tube bank.

8. A tubular oil heater comprising a furnace chamberhaving radiant heatabsorbing transversely spaced oil heating tubes extending along thesides thereof, one of the furnace chamber sides having a heating gasexit occupying a major portion of the area thereof and a plurality ofstaggered rows of relatively widely spaced oil heating tubes extendingacross said gas exit and arranged to receive radiant heat from saidfurnace chamber, means for burning fluid fuel in suspension in saidfurnace chamber, and means supported on the second of said staggeredrows of tubes and partly closing substantially all of the spacestherebetween to form a diffusion baiiie having uniformly distributed gasflow passages of less aggregate flow area than the aggregate intertubearea of the first of said staggered rows of tubes.

9. A tubular oil heater comprising a box-shaped furnace chamber having aheating gas exit occupying a major portion of the roof area thereof anda plurality of staggered rows of relatively widely 5 spaced oil heatingtubes extending across said gas exit and arranged to receive radiantheat from said furnace chamber, means for burning fiuid fuel insuspension in said furnace chamber, and

means supported on the second of said staggered rows of tubes and partlyclosing substantially all of the spaces therebetween to form a diffusionbaifle having uniformly distributed gas flow passages of less aggregateflow area than the aggregate intertube area of the first of saidstaggered rows of tubes.

10. An oil heater comprising a furnace chamber having a heating gas exitoccupying amajor portion of the area of one of the boundary sidesthereof, means for burning fuel in said furnace chamber, inner and outerrows of transversely spaced oil heating tubes extending across said gasexit with the tubes in said inner row in position to receive radiantheat for a major portion of their length from said furnace chamber, andmeans associated with said outer row of tubes forming a diffusion baiiieacross said gas exit having a series of gas flow passages thereinregistering with substantially all of the intertube spaces of said outertube row and of substantially less aggregate flow area than theaggregate intertube area of said inner row of tubes to provide a lowvelocity heating gas flow across the portions of the tubes in said innerrow extending across said gas exit.

11. An oil heater comprising a furnace chamber having a heating gas exitoccupying a major portion of the area of the roof thereof, means forburning fuel in said furnace chamber, upper and lower rows ofhorizontally arranged transversely spaced oil heating tubes extendingacross said gas exit with the tubes in said lower row in position toreceive radiant heat for a major portion of their length from saidfurnace chamber, and means associated with said upper row of tubesforming a diffusion ballie across said gas exit having a series of gasflow passages therein registering with substantially all of theintertube spaces of said upper tube row and of substantially lessaggregate flow area than the aggregate intertube area of said lower rowof tubes to provide a substantially uniform low velocity heating gasflow across the portions of the tubes in said lower row extending acrosssaid gas exit. 1

12. An oil heater comprising a furnace chamber having a heating gasexits occupying a major portion of the area of the roof thereof, meansfor burning fuel in said furnace chamber, upper and lower rows ofhorizontally arranged transversely spaced oil heating tubes extendingacross said gas exit with the tubes in said lower row in position toreceive radiant heat for a major portion of their length from saidfurnace chamber, and bailie tile supported on said upper row of tubesand constructed to form a diffusion baflle across said gas exit having aseries of gas flow passages therein registering with substantially allof the intertube spaces of said upper tube row and of substantially lessaggregate flow area than the aggregate intertube area of said lower rowof tubes to provide a substantially uniform low velocity heating gasflow across the portions of the tubes in said lower row extending acrosssaid gas exit.

13. In a furnace for heating oil, walls, a roof, bare oil heating tubesin said walls and said roof exposed to radiant heat directly from saidfurnace, said roof being open across substantially the entire furnaceexcept for the tubes therein and providing for the exit of combustiongases, and diffusion baffle means extending-across said roof immediatelysuperjacent said roof tubes and providing a uniform velocity of thecombustion gases passing through the roof over said roof tubes. I

14. An oil heater comprising a furnace chamber having a heating gas exitcomprising a major portion of the area of one of the boundary wallsthereof, means for burning fuel in said furnace. chamber, a row ofserially connected bare oil ranged to provide a substantially uniformheat ing gas flow across said tube portions.

15. Ari oil heater comprising a furnace chamb er having a heating gasexit in the roof thereof, means for burning fuel in said furnacechamber, upper and lower rows of transversely spaced oil heating tubesextending across said gas exit with the tubes in said lower row bare andin position to receive radiant heat directly from said furnace chamber,and means associated with said upper row of tubes forming a diffusionbaliie across said gas exit having a series of gas flow passages thereinof substantially less aggregate flow area than the aggregate intertubearea of the portions of the tubes in said lower row extending acrosssaid gas exit and arranged and proportioned to provide a substantiallyuniform heating gas flow across said lower row tube portions.

16. An oil heater comprising a furnace chamber having a heating gas exitcomprising substantially the entire area of the roof thereof, means forburning fuel in said furnace chamber,

groups of serially connected bare oil heating tubes extending alongopposite side walls of said. furnace chamber symmetrically arrangedrelative to said fuel burning means and in position to receive radiantheat over substantially their entire length directly from said furnacechamber, means forming a diffusion baffle across said gas exit having aseries of small gas flow passages substantially uniformly distributedtherein and of substantially less aggregate flow area than said roofarea to provide a substantially uniform low velocity heating gas flowthrough said gas exit, and means forming a plenum chamber at the upperside of said diflusion-bame.

17. An oil heater comprising a furnace chamber having a heating gas exitoccupyin a major portion of the area of one of the boundary wallsthereof, means for burning fuel in said furnace chamber, a row oftransversely spaced bare oil heating tubes extending across said gasexit with the tubes in position to receive radiant heat for asubstantial portion of their length directly from said furnace chamber,means closely adjacent to the outer side of said row forming a diffusionbalile across said gas exit having a series of gas flow passages thereincommunicating with the intertube spaces of said tube row and ofsubstantially less aggregate flow area than the aggregate intertube areaof the portions of the tubes in said row extending across said gas exitand-arranged and proportioned to provide a substantially uniform heatinggas flow across said tube portions, and means forming a plenum chamberat the outer side of said diflusion baflie.

18. An oil heater comprising a box-shaped furnace chamber having aheating as exit occupying substantially the Y entire area of the roofthereof, means for burning fuel in suspension in said furnace chamber,groups of serially connected horizontally extending oil heating tubesarranged along opposite side walls of said furnace chamber, upper andlower rows of transversely spaced oil heating tubes extending acrosssaid gas exit with the tubes in said lower row in position to receiveradiant heat throughout their length from said furnace chamber,"bafllemeans associated with said upper rowof tubes forming a diffusion baffleacross said gas exit having a series of gas flow passagestherein'communieating with the 'intertube'spaces of said upper tube 'rowand of substantially less aggregate flow areathan the aggregateintertube area of said lower row of tubes, means forming a plenumchamber superjacent to said diffusion baille, and a bank of fluidheating tubes arranged to receive heating gases from said plenumchamber.

19. An oil heater comprising walls deflning a furnace of substantiallyrectangular horizontal and vertical cross-section, fuel burner means ina wall of said furnace arranged to project a fluid fuel into saidfurnace, a group of serially conneected horizontally arranged bare oilheating tubes extending along one wall of the furnace, a separate groupof similar tubes extending along the opposite wall of the furnace withsaid tube groups symmetrically arranged relative to said fuel burner'means and in position to receive radiant heat over substantially. theirentire length directly from said furnace, ceramic refractory meanshaving a multiplicity of spaced, relatively small gas exit openingstherein constituting a diffusion bame forming one of the remaining wallsof said furnace with said gas exit openings proportioned and distributedtherein to provide a substantially uniform discharge of heating gasesacross the entire heating gas exit area, means forming a plenum chamberat the outer side of said diffusion baffle, a bank of oil heating tubesabove said plenum chamber and arranged to be heated by convection byheating gases from said plenum chamber, and said fuel burner means, allheating tube groups, and diflusion baiile being relatively arranged toprovide a gas flow from said heating gas exit openings upwardly throughsaid plenum chamber to said convection bank of tubes.

20. An oil heater comprising walls defining a furnace of substantiallyrectangular horizontal and vertical cross-section, fuel burner meansmounted in a vertical wall of said furnace and arranged to project afluid fuel horizontally into said furnace, a group of serially connectedhorizontally arranged bare oil heating tubes extending along one wall ofthe furnace, a separate group of similar tubes extending along theopposite wall of the furnace with said tube groups symmetricallyarranged relative to said fuel burner means and in position to receiveradiant heat over substantially their entire length directly from saidfurnace, ceramic refractory means having a multiplicity of spaced,relatively small gas exit openings therein constituting a radiantlyheated diffusion baiile forming one of the remaining walls of saidfurnace with said gas exit openings proportioned and distributed thereinto provide a substantially uniform discharge of heating gases across theentire heating gas exit area, means forming a plenum chamber at theouter side of said diffusion baiiie, a heating gas flue opening to theupper side of said plenum chamber, a bank of oil heating. tubes in saidheating gas flue arranged to be heated by convection by heating gasesfrom said plenum chamber, and said fuel burner means, oil heating tubegroups, and diffusion baiiie being relatively arranged to provide a gasflow from said heating gas exit opening upwardly through said; plenumchamber to said convection bank of tubes.

21. An oil heater comprising walls defining a furnace of substantiallyrectangular horizontal and vertical cross-section having a floor, fuelburner means in opposite vertical walls of said length, means forming agas exit flue receiving heating gases from all of said oppositelyarranged fuel burner means, a bank of oil heating tubes in said gas exitflue, means forming a plenum chamber between said gas exit flue and saidfurnace, ceramic refractory means having a multiplicity of spacedrelatively small gas exit openings therein and forming a diffusionbaiiie forming one of the remaining walls of said furnace and separatingsaid plenum chamber from said furnace and providing a substantiallyuniform flow of heating gases in said furnace relative to said flrstnamed, groups of oil heating tubes, and said fuel burner means, oilheating tube groups and diffusion baiile being relatively arranged toprovide a heating gas flow through said furnace, diffusion baiile andplenum chamber above the floor level of said furnace and avoid anydownflow of heating gases through said furnace and plenum chamber.-

22. An oil heater comprising walls defining a furnace of substantiallyrectangular horizontal and vertical cross-section having a floor androof, fuel burner means mounted in a wall of said furnace below the roofthereof and arranged to project a fluid fuel .into said furnace, saidwalls defining a heating gas exit forming substantially the entire areaof one of the remaining sides 01' said furnace above the floor thereof,ceramic refractory means having a multiplicity of spaced relativelysmall gas exit openings therein constituting a diffusion bame across theentire'heating gas exit areawith said gas exit openings proportioned anddistributed therein to provide a substantially uniform discharge ofheating gases through all of said gas exit openings, a group of seriallyconnected, horizontally arranged bare .oil heating tubes extending alongone of the remaining vertical walls of the furnace,asecondgroupofserially connected, horizontally arranged bare oil heating; tubesextending along the vertical wall of the furnace opposite to said lastnamed wall with said tube groups symmetricallyarrangedrelative to saiddiffusion baiile and fuel burner means and in position to receiveradiantheat over substantially their entire length directly from saidfurnace, means forming aplenumchamber at the outer side of saiddiifusion baille, aheating gas flue opening to said plenum chamber, abank of oil heating tubes in said heating gas flue arranged to be heatedby convection by heating gases from said plenum chamber, and said fuelburner means, oil heating tube groups and diffusion bailie beingrelatively arranged to provide a heating gas flow through said furnace,diffusion battle. and plenum chamber above the floor level of saidfurnace and avoid any downflow of heating gases through said furnace andplenum chamber.

CARL S. REED. VINCENT W. sum.

